TWI414900B - Exposure method and memory medium storing computer program - Google Patents

Abstract

A method comprises determining an exposure condition by executing a process including computing an image formed on an image plane under the current exposure condition while changing the exposure condition, and evaluating a line width of the computed image, and exposing the substrate under the determined exposure condition, wherein the determining includes, computing a simplified evaluation value of the computed image, changing the exposure condition and executing the process in the changed exposure condition, after evaluating the computed image if the simplified evaluation value satisfies an allowable value, and changing the exposure condition and executing the process in the changed exposure condition without evaluating the computed image if the simplified evaluation value does not satisfy the allowable value.

Description

Exposure method and memory medium for storing computer programs

The present invention relates to an exposure method and a memory medium for storing a computer program.

In the process of the semiconductor device, the exposure process performed by the exposure device is critical in determining the line width of the circuit pattern of the semiconductor device. At the time of the exposure processing, the original is printed by the illumination optical system with light from the light source, and the original pattern is projected onto the photoresist on the substrate via the projection optical system, thereby exposing the photoresist.

With the reduction in the width of the near-call line, an exposure apparatus having a technology that achieves high resolution has been developed. The parameters determining the resolution are the wavelength of the light source, the numerical aperture (NA) of the projection optical system, and the value associated with the process (the so-called process factor K1). In order to achieve high resolution, there is a technique of increasing the NA and lowering the process factor K1. An example of a technique for reducing the process factor K1 is modified illumination, polarized illumination, and aberration adjustment of the projection optics.

Current technologies for achieving high resolution have been diversified and complicated. In this case, in order to transfer the pattern to the substrate with high accuracy, different parameters associated with these techniques are determined. Examples of such parameters are the light intensity distribution on the pupil plane of the illumination optical system (hereinafter referred to as the effective light source distribution), the NA and aberration of the projection optical system, and the polarization state of the illumination light.

In the process of semiconductor devices, in order to determine the capacity of the device (yield One of the most stringent precision factors is dimensional accuracy. As the line width of the pattern is reduced, the dimensional accuracy is getting higher and higher. This has led to an increasing need to optimize various exposure conditions in order to increase the dimensional accuracy to a line width value or lower.

Japanese Patent Publication No. 2004-247737 relates to an optimization method for the shape of an effective light source. More specifically, this patent reference describes an optimization method for an effective light source that divides the effective source into a point source that conforms to the grating pattern and evaluates the segmented point source to optimize the effective source. This patent document also discloses an evaluation method to evaluate the critical dimension (CD), depth of focus (DOF), exposure latitude (EL), depth of focus at 8% exposure latitude (DOF@ 8% EL), dose pair Size ratio (E1:1), dense/isolated shape deviation, and any deviation due to shape size. This patent document also discloses evaluation of side-lobe transfer, film loss, sidewall angle, mask error enhancement factor (MEEF), linear resolution, and absolute resolution.

In the optimization of various parameters, determining the exposure conditions and changing the values of individual parameters throughout the entire range of numbers may take a significant amount of time, which is the number that is expected to be obtained when using these values.

The present invention provides techniques for determining exposure conditions over a short period of time.

One aspect of the present invention provides an exposure method for illuminating an original plate on an object plane of a projection optical system with an illumination optical system so as to project light Forming an image on the image plane of the system, and exposing the substrate on the image plane of the projection optical system, the method comprising: a determining step of determining an exposure condition by performing calculation and evaluation processing, the calculation and evaluation processing The method comprises: calculating a first image formed on an image plane under current exposure conditions and changing an exposure condition, and evaluating a line width of the first calculated image; and an exposure step of exposing the substrate under the determined exposure condition, wherein The determining step includes: calculating a simplified evaluation value of the first calculated image, and if the simplified evaluation value satisfies the allowable value, changing the exposure condition and performing the calculation and evaluation under the changed exposure condition after evaluating the first calculated image Processing, and, if the simplified evaluation value does not satisfy the allowable value, the exposure conditions are changed and the calculation and evaluation process is performed under the changed exposure conditions without evaluating the first calculated image.

Further features of the present invention will become apparent from the description of the embodiments illustrated in the appended claims.

Hereinafter, various embodiments of the present invention will be described with reference to the accompanying drawings.

The process of manufacturing the apparatus will be described with reference to FIGS. 2 and 3. Figure 2 is a flow chart for explaining the manufacturing process of the manufacturing apparatus. Examples of devices are semiconductor wafers such as LSI, IC, and memory, display devices such as liquid crystal panels, and image sensors such as CCD and CMOS sensors. Here, the manufacture of a semiconductor wafer will be described as an example.

In step 1 (circuit design), the circuit of the semiconductor wafer is designed. In step 2 (mask manufacturing), fabricating a circuit diagram on which the design is formed The mask of the case (original). In step 3 (wafer fabrication), a wafer such as tantalum is used to fabricate the wafer. In step 4 (wafer process), called the pre-process, masks and wafers are used to form circuits on the wafer by lithography. In a step 5 (assembly) called a post-process, the wafer fabricated in the step 4 is processed in the form of a wafer to form a semiconductor wafer. This step includes an assembly step (cutting and bonding) and a packaging step (wafer sealing). In the step 6 (inspection), the semiconductor wafer formed in the step 5 is subjected to, for example, an operation confirmation test, a durability test, and the like. In step 7 (shipping), the semiconductor wafer completed in the aforementioned process is shipped.

Here, step 1 (semiconductor design) will be explained. Here, the design of the LSI will be described as an example. When designing an LSI, the system design is first implemented. In the system design, the specifications of the LSI are determined, so that the system is divided into related hardware and software, and the hardware is further divided into blocks. In general, an LSI contains a plurality of blocks. The diversity of these blocks may cover circuits with small logic gates such as flip-flops to large blocks such as CPUs and DSPs. For example, as shown in FIG. 4, an LSI may include, for example, a central processing unit (CPU) 41, a digital signal processor (DSP) 42, a read only memory (ROM) 43, and a random access memory (RAM) 44. Blocks such as logic 45 and 46, analog-to-digital converter (ADC) 47, digital-to-analog converter (DAC) 48, and PLL 49 (also known as macrocells).

Then, the logic design of the LSI is implemented. In logic design, logic circuits are automatically generated that implement the hardware of the system designed by the system design. Finally, the generated level is equal to the circuit element as the semiconductor device The logic circuit of the gate of the transistor.

Then, the layout design of the LSI is implemented. In the layout design, the configuration of the blocks including the logic circuits having the gate level in the LSI wafer is determined, and the interconnections connecting the blocks are designed.

In the embodiment to be described later, information on a circuit pattern (hereinafter referred to as a mask pattern) of the LSI which is laid out in this manner and its pre-design operation is used (hereinafter referred to as layout material). Note that the material obtained by adding the auxiliary pattern can be used, and the auxiliary pattern allows optical approximation effect correction of the mask pattern.

Figure 3 is a flow chart showing the details of the wafer process in step 4. In step 11 (oxidation), the surface of the wafer is oxidized. In step 12 (CVD), an insulating film is formed on the surface of the wafer. In step 13 (electrode formation), an electrode is formed on the wafer by, for example, vapor deposition. In step 14 (ion implantation), ions are implanted into the wafer. In step 15 (resistance process), a photoresist is applied to the wafer. In step 16 (exposure), a circuit pattern of the reticle (original) is projected onto the photoresist-coated wafer to expose the photoresist. In step 17 (development), the exposed photoresist is developed to form a mask pattern. In step 18 (etching), the portion exposed through the opening of the mask pattern is etched. In step 19 (photoresist removal), any unwanted mask patterns remaining after etching are removed. By repeating these steps, a circuit pattern is formed on the wafer.

Next, the exposure apparatus used in the exposure processing in step 16 will be explained with reference to FIG. An optical system including an optical element interposed between the light source 1 and the mask (original) 13 is referred to as an illumination optical system. For example, The light source 1 can be an ultra-high pressure mercury lamp or a quasi-molecular laser that emits light in the ultraviolet or far ultraviolet range. The light emitted by the light source 1 is converted into a target beam shape by the beam shaping optical system 2, and enters the diffractive optical element 3.

The diffractive optical element 3 diffracts the incident light to form a first light distribution of the target on the Fourier transform plane via the Fourier transform lens 4. The diffractive optical element 3 can be interchanged depending on the effective light source distribution to be formed.

The zoom optical system 5 forms an image of the light beam from the first light distribution and the light beam reaching the zoom optical system 5 on the incident surface 6a of the fly-eye lens 6 at a predetermined magnification. The zoom optical system 5 also has a function of adjusting a region where the light beam enters the zoom optical system 5 and the fly-eye lens 6, and thus, illumination conditions such as an effective light source distribution can be changed.

The diffractive optical element 3 and the Fourier transform lens 4 constitute a first optical unit 100, the illumination shape converters 201 and 202 constitute a second optical unit 200, and the zoom optical system 5 constitutes a third optical unit 300. Further, the light intensity distributions composed of the first optical unit 100, the second optical unit 200, and the third optical unit 300 are defined as a first light distribution A, a second light distribution B, and a pupil plane distribution C, respectively. The pupil plane distribution C is synonymous with the angular distribution of incident light on the illumination surface (mask 13) and the effective source distribution.

The effective light source distribution depends on the combination of optical units. A unit directly related to the formation of an effective light source distribution is referred to as an effective light source distribution forming unit. As shown in FIG. 5, the effective light source distribution forming unit is inserted into the diffracted light. The optical element in the optical path between the element 3 and the aperture member 7 is learned.

The first to third optical units 100 to 300 convert the light beam from the light source 1 into a light beam having a shape of a target to adjust the light intensity distribution on the incident surface 6a of the fly-eye lens 6 and the angular distribution of the incident light beam to a target distribution. . By this operation, the light intensity distribution (effective light source distribution) on the pupil plane of the illumination optical system is adjusted.

Next, the second optical unit 200 will be described in detail. In order to form a circular effective light source distribution well known in the art (Fig. 8A), as shown in Fig. 8B, the illumination shape converter may have a concave conical surface (or a flat surface) on its light incident side, and It has a convex conical surface on its light-off side.

In order to form a quadrupole effective light source distribution (Fig. 9A), as shown in Fig. 9B, the illumination shape converter may have a quadrangular pyramid surface (or flat surface) on its incident side and a convex quadrangular pyramid on its departure side. The top of the surface. The angles between the optical axis and the edges of the quadrilateral pyramid of the entrance and exit surfaces of the crucible may be equal or different from one another in order to enhance illumination efficiency (samely applicable to conical ridges). Alternatively, it may be formed by diffring the optical element 3 to form a quadrilateral first light distribution, and providing a conical surface having a concave conical surface (or a flat surface) on its incident side and a convex conical surface on its leaving side. Quadrilateral lighting.

As shown in Figs. 10A and 11A, each of the illumination shape transducer groups is formed in pairs that are relatively movable in the optical axis direction, and more different effective light source distributions can be formed. The pair of turns shown in Figures 10A and 11A comprises a crucible having a concave conical incident surface and a flat exit surface, and a crucible having a flat incident surface and a convex conical leaving surface. As shown in Figure 10B If the interval between the turns is small, an annular effective light source distribution having a light-emitting portion having a large width (having a large annular portion ratio) is formed. On the other hand, as shown in Fig. 11B, if the interval between the turns is large, an annular effective light source distribution having a light-emitting portion having a small width (having a small annular portion ratio) is formed.

Next, the third optical unit 300 will be described in detail. Figure 12A shows an example of the light intensity of a profile of an effective source distribution. By adjusting the zoom optical system 5 constituting the third optical unit 300 in response to the dimensional change of the effective light source distribution, the sectional light intensity can be changed from the state shown in Fig. 12A to the state shown in Fig. 12B. At this time, the effective light source distribution can be changed from the state shown in FIG. 12C to the state shown in FIG. 12D. The zoom optical system 5 can be grouped to adjust the size (σ value) of the effective light source distribution and maintain a given annular zone ratio.

For example, to form an annular effective source distribution (FIG. 8A) having the above configuration, the first optical unit 100 forms a circular first light distribution A. The second optical unit 200 also forms an annular second light distribution B. Then, by driving the optical element (稜鏡) in the second optical unit 200, the ratio of the annular region (the quotient of the inner diameter (inner σ) of the ring divided by the outer diameter (outer σ) can be adjusted) . Further, the third optical unit 300 can adjust the size of the effective light source distribution and maintain a given shape of the second light distribution.

The fly-eye lens 6 is configured by a plurality of microlenses arranged in a two-dimensional array, and has a leaving surface corresponding to the pupil plane of the illumination optical system and having a pupil plane distribution formed thereon (effective light source distribution). By obscuring any unwanted light to form a target distribution The member 7 is located on the pupil plane of the illumination optical system. The aperture member 7 has its aperture size and shape adjusted by a diaphragm drive mechanism (not shown).

The illumination lens 8 illuminates the field stop 9 with the light intensity distribution on the incident surface 6a of the fly-eye lens 6. The field stop 9 includes a plurality of movable visors, and an exposure range on the surface of the mask 13 (finally, the surface of the wafer 15) used as the surface of the illuminating target to form an arbitrary field of view pupil 9 Aperture shape. The imaging lenses 10 and 11 project the aperture shape of the field stop 9 to the mask 13. The deflecting mirror 12 biases the optical path between the imaging lenses 10 and 11.

The mask (original) 13 is held by the mask stand 17, and the mask stand 17 is driven by a mask stage driving device (not shown).

The projection optical system 14 forms an image of the pattern of the reticle 13 on the wafer (substrate) 15 to expose the wafer 15, and the reticle 13 is illuminated by the illumination optical system. When the mask 13 and the mask stage 17 are retracted from the optical path, a light amount distribution (light intensity distribution) similar to the effective light source distribution is formed on the pupil plane of the projection optical system 14. Note that the effective light source distribution corresponds to the angular distribution of the exposure light striking the surface of the mask 13, and the light amount distribution (light intensity) formed on the pupil plane of the projection optical system 14 when the mask 13 is not located on the object plane. Distribution) related. It is also noted that the pupil plane of the projection optical system 14 is optically conjugate with the pupil plane of the illumination optics.

The wafer 15 is held by the wafer table 18, and the wafer table 18 moves in the optical axis direction of the projection optical system 14 and along a plane perpendicular to the optical axis. mobile. The wafer table 18 is driven by a wafer table drive (not shown).

The detector 16 is mounted on the wafer table 18 to detect the amount of exposure impinging on the plane on which the wafer 15 is located. Wafer table 18 is driven such that detector 16 moves along the plane on which wafer 15 is located. At this time, the signal detected by the detector 16 is sent to the main controller 20.

The main controller 20 adjusts the effective light source distribution by controlling the actuator 22.

In accordance with a command from the main controller 20, the controller 21 controls the driving of the optical elements 14a to 14d in the projection optical system 14 and the aberration of the projection optical system 14. In accordance with another command from the main controller 20, the controller 21 controls the NA diaphragm 14e disposed in the pupil plane of the projection optical system 14 to adjust the NA of the projection optical system 14. The main controller 20 is connected to the computer 30.

FIG. 6 is a block diagram showing an example of the configuration of the computer 30. The computer 30 executes a program for determining an exposure condition. The computer 30 includes a control unit 31, a storage unit 32, a bridge 33, an output interface 34, a network interface 35, and an input interface 36. The control unit 31, the storage unit 32, the output interface 34, the network interface 35, and the input interface 36 are individually connected to the bridge 33 via busbars. Output interface 34 is coupled to display 37 and input interface 36 is coupled to input device 38. The network interface 35 is connected to a network such as a local area network (LAN), and thus can communicate with other computers. The network interface 35 is also connected to the main controller 20 of the exposure device.

For example, the controller unit 31 may include a CPU (Central Processing Unit), a DSP (Digital Signal Processor), an FPGA (Field Programmable Gate Array), and a microcomputer. The storage unit 32 can include a memory such as a ROM and a RAM. Input device 38 can include a mouse and a keyboard. The control unit 31 executes a computer program (software code) stored in the storage unit 32 to control the operation of the computer 30 for use as a device for executing a process or method according to a computer program. Via the output interface 34, the processing results of the computer program can be output to the display 37, other output devices, and/or the main controller 20. The storage unit 32 can store not only the computer program, but also the NA of the device to be manufactured, the layout data, the types, combinations, parameters, restriction information, and effective light source distribution of the constituent elements of the illumination optical system, and the image of the projection optical system. Poor information. The layout information and the aberration information of the projection optical system can be provided to the computer 30 via the network interface 35 and stored in the storage unit 32. The computer program can be installed on the computer 30 via a memory medium or a network.

1 is a flow chart showing a sequence of a method of determining exposure conditions according to the first embodiment. More precisely, the control unit 31 operates in accordance with a computer program (software code) stored in the storage unit 32, thereby executing the program shown in this flowchart. Hereinafter, a method of determining an exposure condition will be described with reference to FIGS. 1, 7A to 7D, 13A, and 13B.

First, in step S101, a mask pattern (original pattern) is set. More specifically, in step S101, a mask pattern for determining an exposure condition is set. This mask pattern is typically used for evaluation purposes only, but can also be used to make real devices. For example, as shown in FIGS. 13A and 13B, The mask pattern is an L/S (line and space) pattern, and the line and space width is 80 nm to illustrate the present embodiment. Fig. 7C is a view exemplifying an image formed on the image plane of the projection optical system 14 when the mask pattern shown in Figs. 13A and 13B is illuminated with the effective light source distribution shown in Fig. 7A. FIG. 7D is a diagram illustrating an image formed on the image plane of the projection optical system 14 when the mask pattern shown in FIGS. 13A and 13B is illuminated with the effective light source distribution shown in FIG. 7B.

In step S102, a fixed value at the time of optimization is set to calculate an image formed on the image plane of the projection optical system 14 (the plane on which the wafer 15 is located). For example, the NA of the projection optical system 14, the wavelength of the exposure light, and the aberration of the projection optical system 14 can be set. Unique parameters can be set to calculate the image. For example, the unique parameters may include a number of segments for Fourier transform to calculate the image, and a photoresist specific parameter when the photoresist image is to be taken.

Here, for example, it is assumed that the exposure light has a wavelength of 193 nm, the projection optical system 14 has an NA (numerical aperture) of about 0.85, and the ring illumination used has a ring-area ratio of 1/2. Further, it is assumed that the resist (photoresist) has a refractive index of about 1.7.

In step S103, an initial value is set as a parameter of the exposure condition to be optimized. For example, the initial value of the outer σ of the ring illumination can be set to 0.8.

In step S104, an evaluation condition is set. More specifically, an evaluation point on the mask pattern, an evaluation equation for calculating an evaluation value used to determine the exposure condition, and an allowable value at the time of evaluation can be set. Figure 13A As shown in 13B, the evaluation point setting can be the center line width CDc and the end line widths CD1 and CDr. The center line width is the width of the line at the center of the L/S pattern, and the end line width is the width of the line at the end of the L/s pattern. The difference between the line widths CDc, CD1, and CDr and their target line widths is defined as ΔCDc, ΔCD1, and ΔCDr, respectively.

As the evaluation value setting, the evaluation value ΔCD_RMS calculated by the following evaluation equation is used in the present embodiment: ΔCD_RMS = {(ΔCDc ² + ΔCD1 ² + ΔCDr ² ) / 3} ^1/2 ... (1)

The allowable value at the time of evaluation can be set as a condition in which, for example, the difference with respect to the target line width is less than or equal to 10 nm.

In step S105, an effective light source distribution is set. When the step S105 is performed for the first time after the step S103, the effective light source distribution corresponding to the initial value set in the step S103 is set. In step S105 subsequent to step S112, an effective light source distribution corresponding to the option (exposure condition) for the effective light source distribution changed in step S112 is set. In the present embodiment, the effective light source distribution is optimized and the outer σ is changed in step S112.

For example, the effective light source distribution can be optimized based on the constraints given by the illumination optics. More specifically, optimization can be performed within the range of the effective light source distribution by selecting the optical unit shown in FIGS. 8A, 8B, 9A, and 9B, and adjusting FIGS. 10A, 10B, 11A, and 11B. The spacing between the two turns shown, as well as adjusting the zoom optics 5, can form a range of effective light source distributions. Illumination optics The limits given by the system mean the range of effective light source distributions that can be achieved by the action of current exposure devices. However, if a new function can be incorporated into the illumination optics, it can also be set to be optimized. For example, the shape of the ridge defined by the angle of the ridge edge with respect to the optical axis, etc., may be optimized.

By optimizing the effective light source distribution, an ideal distribution can be found. A typical example of the method of obtaining this ideal distribution is a method of making the light intensity uniform, and represented by parameters such as external σ, ring ratio, aperture angle, and aperture size, and using a representation (for example, a polynomial, an exponential function). , Gaussian distribution, or other distribution function) to illustrate a component of the light intensity distribution, and a method of representing the parameters by the coefficients of the representation string.

The exposure conditions to be optimized include not only the effective light source distribution, but also all of the various parameters that can be adjusted and changed during exposure. Examples of optimization targets are the polarization distribution of illumination light, the center wavelength of illumination light, the spectral shape of illumination light (information containing superimposed shapes of multiple different wavelengths), NA, aberrations, and the pupil of the projection optical system. Transmittance distribution, and angular characteristics of reflectivity on the surface of the resist.

In step S106 (image calculation step), the pattern image formed on the image plane of the projection optical system 14 under the set conditions (including the current effective light source distribution) is calculated by optical simulation. More specifically, the reticle pattern on the object plane of the reticle pattern on the object plane of the projection optical system 14 is illuminated by the illumination optical system to be formed on the image plane (wafer surface) by the projection optical system 14. Image (light intensity distribution). This image is often referred to as an aerial image or an optical image.

In step S107, it is checked whether the simplified evaluation value (light intensity distribution) of the aerial image satisfies the critical value. If YES in step S107, the process proceeds to step S108. If NO in step S107, the process proceeds to step S112. An example of the simplified evaluation target is a cross-sectional view of the aerial image (light intensity distribution) in the direction of the evaluation points CDc, CD1, and CDr set in the evaluation step S104. An example of a simplified evaluation value may be the minimum NILS (normalized image log slope) value of the NILS values taken at the three evaluation points CDc, CD1, and CDr. As is well known to those skilled in the art, NILS values can be calculated according to the following equation: Where I is the light intensity and lnI is the natural logarithm of the light intensity I.

The NILS value calculated as the simplified evaluation calculation in step S107 is illustrated by taking N1 as an example in FIG. Moreover, the critical value is illustrated by taking N2 as an example in FIG.

It is assumed that the critical value N2 is 0.8. In this case, if the effective light source distribution group in the example shown in Fig. 16 has an outer σ of 0.60 or less (indicated by "Sigma_out" in Fig. 16), the NILS value as a simplified evaluation value is not The critical value N2 is satisfied, and is determined to be NO in step S107. Then, in step S112, another option for the effective light source distribution is set, and step S105 and its subsequent steps (i.e., a sequence of optimization procedures) are performed again. On the other hand, let's say Figure 16. In the example shown in the example, the effective light source distribution group has an outer σ of 0.65 or higher, and the NILS value as the simplified evaluation value satisfies the critical value N2, and is judged as YES in step S107. Then, the process proceeds to step S108.

In this manner, in the present embodiment, the given exposure condition in which the simplified evaluation value does not satisfy the critical value becomes another exposure condition, and the evaluation value for a given exposure condition (described later) is not calculated, and The optimization calculation continues. According to this operation, since the evaluation value for which the simplified evaluation value does not satisfy the critical value (the evaluation value for this exposure condition does not naturally satisfy the evaluation criteria) calculates the evaluation value, the overall time for optimizing the calculation shorten. As is clear from the gist of the above description, the simplified evaluation value is used as an evaluation index, and the simplified evaluation value (described later) can be calculated at a time shorter than the time taken to calculate the evaluation value.

Although the minimum NILS value of the NILS value obtained at the three evaluation points is selected as the simplified evaluation value in the present embodiment, the NILS value of the pattern having the smallest half pitch of all the patterns appearing on the same mask can be selected. Decided to simplify the evaluation value.

The simplified evaluation value only needs to allow the intensity level assessment of the light intensity distribution, and in addition to the NILS value, various evaluation values can be selected as the simplified evaluation value. For example, the simplified evaluation value may be an imaging contrast value Cnt or ILS (image log slope) value respectively given by the following equation: Cnt = (Imax - Imin) / (Imax + Imin) (3)

If the NILS value is used as a simplified evaluation value, the threshold value N2 can be set within the range of 0.5 ≦ N2 ≦ 20 according to the process. If the comparison value Cnt is used as the simplified evaluation value, the threshold value Cnt2 can be set within the range of 0.25 ≦ Cnt2 ≦ 0.6 according to the process. If the ILS value is used as the simplified evaluation value, the threshold value I2 can be set within the range of 1 ≦ I2 ≦ 50 [1/μm] according to the process.

In step S108, the pattern line widths CDc, CD1, and CDr are calculated based on the aerial images calculated in step S106 for each evaluation point. This calculation can take advantage of the fixed slice model, which is the simplest model of the commonly used model. The fixed slice model is used to define the intersection between the aerial image and the slice level of a certain light intensity as the two edges of the line width, and the aerial image is sliced at the intersection. The slice level can be selected such that the line width of the central pattern is the target value.

In step S109 (evaluation step), based on the line widths CDc, CD1, and CDr calculated in step S108 and the target size of 80 nm, the evaluation value ΔCD_RMS is calculated according to the following equation: ΔCDc = CDc - 80 ΔCD1 = CD1 80 ΔCDr=CDr-80 ΔCD_RMS={(ΔCDc ² +ΔCD1 ² +ΔCDr ² )/3} ^1/2 ...(5)

In Figure 16, the evaluation of each effective source distribution is indicated by C1. Note that for ease of explanation, FIG. 16 also shows an evaluation value Δ of the effective light source distribution having the NILS value for satisfying the critical value N2. CD_RMS.

In step S110, it is checked whether the evaluation value calculated in step S109 falls within the allowable value and whether it is the optimum value of the evaluation value calculated for the plurality of exposure conditions (effective light source). If the smaller the evaluation value is, the optimal value is the minimum value. If the larger the evaluation value is, the optimal value is the maximum value. Alternatively, the optimal value can be a specific value. If the RMS value ΔCD_RMS is used as the evaluation value, since the RMS value is a remainder with respect to the target line width, the optimum value is the minimum value.

As shown in Figure 16, it is assumed that there are six options for effective light source distribution. In this case, when the effective light source distribution corresponding to the NILS value N1 greater than the threshold value N2 (that is, the effective light source distribution determined to be YES in step S107) has an outer σ=0.65 and an inner σ=0.325 and When the effective light source distribution presenting the minimum evaluation value is specified, it is determined to be YES in step S110. Then, in step S111, the specified effective light source distribution is determined as an exposure condition.

Note that if the threshold value N2 is not set for the NILS value, the effective light source distribution with the outer σ=0.55 and the inner σ=0.275 exhibits the minimum evaluation value, but it can be expected that selecting this distribution will deteriorate the capacity of the device to be manufactured. .

In step S108, the VTR or VBR obtained by the influence of the resist processing on the patterned wafer or the convolution integration of the optical image when the optical image is shifted may be obtained. The photoresist model is used to calculate the line width. Note that VTR and VBR are abbreviations for "variable threshold photoresist model" and "variable offset photoresist model", respectively. .

Conditions can be set to prevent endless repeated calculations, in which, in the case where the number of executions determined in step S110 reaches the specified number, although the simplified evaluation value does not satisfy the allowable value, the processing is terminated. In this case, the optimization calculation is performed again by changing at least one of steps S104, S103, S102, and S101.

In this way, the degree of intensity of the light intensity distribution is used as a simplified evaluation value, which not only allows shortening of the overall time for optimization, but also allows for the determination of an effective light source distribution that ensures a given exposure tolerance.

The exposure conditions optimized using the computer 30 are supplied to the main controller 20, which sets the exposure conditions by controlling the actuator 22. This enables the formation of the target imaging pattern on the wafer as well as ensuring a given exposure tolerance.

Next, a second embodiment of the present invention will be explained. Note that details not specifically indicated herein may be the same as the first embodiment. The main difference from the first embodiment will be explained.

14A and 14B are flowcharts showing a sequence of a method of determining exposure conditions according to the second embodiment. More precisely, the control unit 31 operates in accordance with a computer program (software code) stored in the storage unit 32, thereby executing the processing shown in this flowchart. This embodiment provides a determination of the effective source distribution that primarily optimizes the CD-DOF.

The CD-DOF is a parameter that takes a processing error as an example and serves as an index indicating the defocus tolerance in the exposure apparatus. Here, the value of DOF (focus depth) when the CD is less than 10% of the allowable value is set as a real CD-DOF example.

Figure 15 illustrates a CD with an isolation pattern when the exposure light has a wavelength of about 193 nm, the projection optical system has a numerical aperture (NA) of about 0.85, and the ring illumination used has an external σ of about 0.7 and an internal σ of about 0.467. -DOF. In Fig. 15, the horizontal axis represents the defocus amount, and the vertical axis represents the line width. For example, a function of these variables is adapted in a polynomial. The range within which the adapted curve falls within about ±10% (in this case, 85 nm) of the target line width is defined as DOF.

After the effective light source distribution is calculated in step S105, the pattern image at the optimal focus position is calculated in step S120. Note that the processing in step S120 is the same as the processing in step S106 in the first embodiment.

In step S121, it is checked whether the simplified evaluation value of the aerial image (light intensity distribution) calculated in step S120 satisfies the critical value. If YES in step S121, the process proceeds to step S122. If NO in step S121, the process proceeds to step S112. An example of a simplified evaluation value may be the minimum NILS value of the NILS value taken at the three evaluation points CDc, CD1, and CDr. If the NILS value as the simplified evaluation value does not satisfy the critical value N2, it is determined to be NO in step S121. In this case, another option for the effective light source distribution is set. On the other hand, if the NILS value as the simplified evaluation value satisfies the critical value N2, it is judged as YES in step S121, and the processing proceeds to step S122.

In this manner, in the present embodiment, the given exposure condition in which the simplified evaluation value does not satisfy the critical value becomes another exposure condition without calculating the optimum focus line width (S122) and defocus evaluation for a given exposure condition. (S123 To S125), and, the optimization calculation continues. By doing so, the overall time for optimizing the calculation can be shortened.

At this time, if the NILS value of the best-focused image that is expected to have the largest contrast is less than the critical value, then the NILS value of the defocused image can be predicted to be naturally smaller than the critical value. In this case, as described above, the given exposure condition in which the simplified evaluation value does not satisfy the critical value is changed to another exposure condition without performing the line width calculation for performing the best focus for the given exposure condition (S122) and Defocus evaluation (S123 to S125), and optimization is continued.

In step S123 (second image calculation step), a pattern formed on a plane deviating from the image plane (defocus plane) of the projection optical system 14 under the set condition (including the current effective light source distribution) is calculated by optical simulation. image.

In step S124, the line width of the defocus pattern image is calculated. In step S125, it is checked whether the defocus amount has reached the specified amount. If YES in step S125, the process proceeds to step S109. If NO in step S215, another defocus amount is set in step S126, and in step S123, the pattern image is again calculated.

In step S109, an evaluation value (for example, DOF) is calculated based on the line widths calculated in steps S122 and S124.

In step S110, it is checked whether the evaluation value calculated in step S109 falls within the latitude and whether it is the optimum value among the evaluation values calculated for the plurality of exposure conditions (effective light source distribution). When the effective light source distribution that exhibits the best evaluation value within the latitude is specified, it is determined in step S110. Yes. Then, the specified effective light source distribution is determined as the exposure condition in step S111. By the above processing, it is possible to determine the effective light source distribution that allows the maximum DOF to be obtained.

In this way, when optimization is performed by considering the line width at the time of defocusing and the line width at the time of optimal focusing, the optimization time is lengthened due to a large amount of calculation. Therefore, it is possible to change a given exposure condition in which the simplified evaluation value does not satisfy the critical value to another exposure condition without performing any optimization processing for a given exposure condition, and to continue the optimization calculation.

When evaluated according to the ED-window (exposure dose window), for each defocus amount setting, the pattern line width at which the exposure amount is increased and decreased by 10% with respect to the slice level is calculated.

The ED-window in which the line width is still smaller than the allowable value even when the exposure amount is changed by 10% is defined as DOF, and therefore, the DE-window is an evaluation value that more strictly evaluates the fluctuation factor in the exposure processing. As in the embodiment of the above evaluation value, generally, by introducing an ED-window as an evaluation amount and setting it as a critical value to evaluate the intensity level of the light intensity distribution having the optimum exposure amount at the time of optimal focusing, it is decided The efficiency of the exposure conditions is greatly increased.

As described above, according to the present embodiment, the overall time for optimization can be shortened when the exposure condition is determined based on the evaluation value including the DOF.

While the invention has been described with reference to the embodiments illustrated in the embodiments, the invention The scope of the appended claims is based on the broadest interpretation to cover all such modifications and equivalent structures and functions.

1‧‧‧Light source

2‧‧‧ Beam shaping optical system

3‧‧‧Diffractive optical components

4‧‧‧ Fourier conversion lens

5‧‧‧Zoom optical system

6‧‧‧Future eye lens

6a‧‧‧ incident surface

7‧‧‧Photographic components

8‧‧‧ Illumination lens

9‧‧‧ Field of view

10‧‧‧ imaging lens

11‧‧‧ imaging lens

12‧‧‧ deflection mirror

13‧‧‧ mask

14‧‧‧Projection optical system

14a‧‧‧Optical components

14b‧‧‧Optical components

14c‧‧‧Optical components

14d‧‧‧Optical components

14e‧‧‧NA Light

15‧‧‧ wafer

16‧‧‧Detector

17‧‧‧ masking table

18‧‧‧ Wafer

20‧‧‧Master controller

21‧‧‧ Controller

22‧‧‧Actuator

30‧‧‧ computer

31‧‧‧Control unit

32‧‧‧ storage unit

33‧‧‧ Bridge

34‧‧‧Output interface

35‧‧‧Internet interface

36‧‧‧Input interface

37‧‧‧Display

38‧‧‧Input device

41‧‧‧Central Processing Unit

42‧‧‧Digital Signal Processor

43‧‧‧Reading memory

44‧‧‧ Random access memory

45‧‧‧Logic

46‧‧‧Logic

47‧‧‧ Analog-to-digital converter

48‧‧‧Digital to analog converter

100‧‧‧First optical unit

200‧‧‧Second optical unit

201‧‧‧Lighting shape converter

202‧‧‧Lighting shape converter

300‧‧‧ Third optical unit

1 is a flow chart showing a sequence of a method of determining exposure conditions according to a first embodiment; FIG. 2 is a flow chart illustrating a device manufacturing method; FIG. 3 is a flow chart illustrating a device manufacturing method; The layout of the LSI block is illustrated; FIG. 5 is a view illustrating a configuration of an exposure apparatus according to an embodiment of the present invention; and FIG. 6 is a block diagram showing a configuration example of a computer that executes a program that determines an exposure condition; FIGS. 7A to 7D Is a view for explaining a representative relationship between an effective light source distribution and an image formed on an image plane of the projection optical system; FIG. 8A is a view illustrating an effective light source distribution of the annular illumination; FIG. 8B is a view, illustrating A conical enthalpy for forming a distribution as shown in FIG. 8A; FIG. 9A is a view illustrating an effective light source distribution in multi-pole illumination; FIG. 9B is a view illustrating an example for forming a distribution as shown in FIG. 9A Fig. 10A is a view illustrating a configuration of a conical ridge; Fig. 10B is a view illustrating an effective light source distribution corresponding to the configuration shown in Fig. 10A, and Fig. 11A is a view FIG. 11B is a view showing another configuration of the conical ridge; FIG. 11B is a view showing the configuration corresponding to the configuration shown in FIG. 11A. FIG. 12A to FIG. 12B are diagrams illustrating an effective light source distribution; FIGS. 13A and 13B are views illustrating a mask pattern; FIGS. 14A and 14B are flowcharts showing a sequence of a method of determining exposure conditions according to the second embodiment; Fig. 15 illustrates a CD-DOF according to the second embodiment; and Fig. 16 is a bar graph illustrating evaluation values and simplified evaluation values corresponding to changes in the effective light source in the first embodiment.

Claims (6)

A method of determining an exposure condition used in an exposure apparatus, the exposure apparatus exposing a substrate by illuminating an original with an illumination optical system such that a pattern of the master is projected onto the substrate by a projection optical system, the method comprising : setting a tentative value for determining an exposure condition of the exposure condition value; setting a simplified evaluation condition for evaluating the intensity level of the light intensity distribution in the image plane of the projection optical system and evaluating the image plane on the image plane a line width evaluation condition of the line width of the formed image; the tentative value is used to calculate a light intensity distribution in the image plane, and the calculation is simplified by evaluating the calculated light intensity distribution and the simplified evaluation condition Evaluating a value; calculating a line width of the image formed on the image plane, and if the simplified evaluation value satisfies the first allowable value, by evaluating the calculated line width and the line width evaluation condition Calculating a line width evaluation value; and if the line width evaluation value satisfies a second allowable value, determining the exposure condition value; wherein the exposure condition The provisional value is changed, and the calculation of the light intensity distribution is performed again using the tentative value of the change of the exposure condition, but if the simplified evaluation value does not satisfy the first allowable value, the calculation is not performed. a line width, wherein the tentative value of the exposure condition is changed if the simplified evaluation value satisfies the first allowable value, but the line width evaluation value does not satisfy the second allowable value. The method of claim 1, wherein the simplified evaluation value is one of a NILS value, an ILD value, and a comparison value of a light intensity distribution in the image plane. The method of claim 1, wherein the line width of the image is calculated to include a line width of an image formed at a plane deviating from the plane of the image, and by evaluating the image formed on the image plane The line width evaluation value is calculated by the image and the image formed at the plane deviating from the image plane and the line width evaluation condition. The method of claim 1, wherein the exposure condition comprises lighting conditions. The method of claim 1, wherein the exposure condition comprises an effective light source distribution. A memory medium storing a computer program causing a computer to perform a method of determining an exposure condition used in an exposure apparatus, the exposure apparatus exposing a substrate by illuminating an original with an illumination optical system, such that the projection optical system And projecting the original pattern onto the substrate, the method comprising: setting a tentative value of an exposure condition for determining an exposure condition value; setting a strength level for evaluating a light intensity distribution in an image plane of the projection optical system a simplified evaluation condition and a line width evaluation condition for evaluating a line width of an image formed on the image plane; the tentative value is used to calculate a light intensity distribution in the image plane, and the calculation is performed by evaluating the The light intensity distribution and the simplified evaluation condition are used to calculate a simplified evaluation value; Calculating a line width of the image formed on the image plane, and if the simplified evaluation value satisfies the first allowable value, calculating the line width by evaluating the calculated line width and the line width evaluation condition Evaluating the value; and determining the exposure condition value if the line width evaluation value satisfies the second allowable value; wherein the tentative value of the exposure condition is changed, and performing the tentative value of the change of the exposure condition again Calculating the light intensity distribution, but if the simplified evaluation value does not satisfy the first allowable value, the line width is not calculated, wherein if the simplified evaluation value satisfies the first allowable value, If the line width evaluation value does not satisfy the second allowable value, the tentative value of the exposure condition is changed.